As the technology for printing develops and the quality of printed materials continues to improve, the need for more accurate and flexible finishing operations on printed material such as box packaging, point-of-purchase displays, or other such products has increased. Finishing operations include such processes as creasing (creating a fold line) and cutting.
Creasing, typically carried out using a creasing wheel or creasing shoe made of steel, must be done from the side opposite to the printed side of a sheet in order to avoid damaging the printed media and to create a fold which will both hold better when the product, such as a box, is formed, and give the final product a higher quality appearance.
Finish cutting of thicker printed sheet material is another example of a finishing operation which is preferably done from the side of the sheet opposite to that on which graphics have been printed. Such cutting is typically carried out using long oscillating blades. When cutting is done from the printed side, cut lines often cross to some extent, degrading appearance and resulting in a lower quality final product. These cut crossings usually occur at inside corners or corners with small radii. By cutting from the side opposite to the printed side, these small imperfections are concealed, thus improving the quality of the final product.
In order to produce such high quality results, it is necessary that such finishing operations operate with high-accuracy registration between the graphics on the printed side (herein called the graphics side) and the folds or cuts produced by the finishing operation carried out from the opposite side (herein called the process side).
Such finishing operations are often done using tools attached to the head of a flatbed X-Y plotter. Methods and associated apparatus which are able to achieve high-accuracy control during the processing of sheet material are part of the i-cut™ vision cutting system from Mikkelsen Graphic Engineering of Lake Geneva, Wis., USA, and is the subject of U.S. patent application Ser. No. 09/678,594, filed on Oct. 4, 2000, Ser. No. 10/283,460, filed on Oct. 30, 2002, and U.S. Pat. Nos. 6,619,167, 6,619,168, and 6,672,187. All of these documents disclose methods and/or apparatus which address high-accuracy processing of graphics sheet material more broadly defined as “narrow-path processing.”
The invention described in Ser. No. 09/678,594 is a method and apparatus for achieving highly improved accuracy in cutting around graphics areas in order to fully adjust for distortion in the sheets from which the graphics areas will be cut, including distortion of differing degrees in different directions on the sheet of material. The distortion may be from the printing process or from some other post-printing process such as material handling or during the cutting process itself. This invention also provides improved speed and accuracy in narrow-path-processing and greater efficiency of material usage.
The invention disclosed in U.S. Pat. No. 6,619,167 is a method and apparatus for automatically and rapidly determining the position and orientation of a sheet of material on a work surface. When the placement of the sheet of material is not precisely controlled, the speed of the cutting or other narrow-path-processing system is often impaired because the system may require manual intervention to adjust the placement of the sheet of material so that the system can begin processing. Thus, the invention described in such patent disclosure provides further improved speed over the invention described in the first-mentioned patent disclosure.
The invention disclosed in U.S. Pat. No. 6,619,168 is a method and apparatus which further improves the speed and efficiency of narrow-path-processing by automatically correcting for careless initial manual placement or malfunctioning automatic placement of a sheet of material on a work surface. The invention automatically and rapidly finds a set of special marks used for determination of the position and orientation of the sheet of material, eliminating the need for yet another possible manual intervention step.
The invention disclosed in U.S. Pat. No. 6,672,187 extends the capability of the Mikkelsen Graphic Engineering's i-cut™ vision cutting system, enabling the position and orientation of the sheet of material to be determined without the use of special marks.
Prior to the invention described herein, any attempt to perform finishing operations, such as the cutting and creasing operations described above, from the process side would have required determining the position and orientation of the sheet only from the sensing of the corners or edges of the graphics sheets from the process side of the sheet. Such an approach would not be able to compensate for variations in print registration or distortion of the sheet material and would provide no control of the process to prevent applying the wrong set of finishing operation instructions to a sheet of material.
One approach which has achieved limited success has been to drill holes through the sheet of material from the graphics side based on the positions of registration marks and then to finish-process the sheet from the process side based on the position of these holes. This method is both costly and inefficient.
Thus there is a need for a highly accurate, fast, and flexible method, apparatus, and system for finish-processing of graphics sheets from the side opposite to the printed side of the sheet.